26 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 68 



Turning- to figure 8, there will be seen ;i re])roduction of a record 

 of the deflections of the galvanometer needle which measures the 

 amount of energy absorbed by the blackened bolometer strip, as there 

 passes over it. under varied circumstances, the i5°-prismatic rock- 

 salt spectrum of the lamp of 88 Nernst filaments or glowers. This 

 record was made September 19, 1916, with 0.012 cm. ppt. HoO in the 

 path between th^ lamp and the bolometer. 



The record consists of three sets of curves : first a lower, dotted, 

 single-branched record indicating" the zero of the galvanometer 

 needle when a shutter at a temperature of about 300° K. was inserted 

 between the lamp and the slit ; second, an upper, five-branched curve, 



Fig. 8. — Bologram 15° rock-salt pri.smatic spectrum of Nernst lamp 

 through aqueous vapor and carbon dioxide in the spectroscopic path alone. 

 7 grams CO- in m^ path, 0.012 cm. ppt. H2O. 



abcdc, the observed energy spectrum of the lamp. The branch 

 shows the rapid rise of energy to a maximum at 1.838 /x and, for the 

 present record, was made with a slit 0.67 mm. wide, the inflowing" 

 energy being further reduced i/20th by a rotating- sector. There is 

 a rapid fall of energy on the right-hand or long- wave-length side, 

 and the sector was removed to allow sufficient energy to flow through 

 the slit to produce the branch b ; then for the branch c the slit was 

 increased to 2.36 mm., for the branch d to 5.82 mm., and finallv for the 

 branch e to 10.69 "I'ti-^ 



^ These slit-widths were obtained cither by the use of brass slits of fixed 

 widths inserted in front of the regular spectroscope slit, or by closing the 

 latter until its jaws just touched a measured cylindrical template. 



